Re: [PATCH 04/23] sim/erc32: Add FPU support on x86_64 hosts.

Mike Frysinger
2015-02-22T04:40:19Z

[-- Attachment #1: Type: text/plain, Size: 1088 bytes --]

On 19 Feb 2015 21:45, Jiri Gaisler wrote:
> On 02/17/2015 10:05 AM, Mike Frysinger wrote:
> > On 17 Feb 2015 08:44, Jiri Gaisler wrote:
> >> * float.c (get_accex) access FPU control and status words on x64
> >
> > shouldn't you gut this file and use <fenv.h> instead for a portable method ?
> > http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/fenv.h.html
> >
> > at the very least, you could cut over to <fpu_control.h> ...
>
> I will switch to fenv.h, but this will produce less accurate results
> on Intel hardware. double on SPARC V8 has 53-bit mantissa while Intel has
> both 53- and 64-bit, and 64-bit is default. To get accurate SPARC V8 FPU
> operations, the Intel FPU should be switched to 53-bit, but the fenv.h
> does not have an API for this. I guess we will have to live with that ...

if you wanted to keep a little inline asm to just that particular bit twiddle,
that should be fine.

normally the sims are functional ... but i guess this part of the simulator is
relying on the inaccuracies of floating point to trade for speed ?
-mike

[-- Attachment #2: Digital signature --]
[-- Type: application/pgp-signature, Size: 819 bytes --]